Someone recommended getting the Oyster Card, but you might check to see if the London TravelCard may be better for you. The TravelCards are only available to people visiting from outside the UK and can be cheaper than getting an Oyster Card. Here is a side-by-side comparison. Note that the TravelCard can also be purchased through the AAA.
Check with your bank and your credit card companies for their foriegn exchange fees and use the best card for your purchases and walkabout cash. Please check NOW--you don't want to find out that your cards are unusable overseas when you get there. You might avoid the convenience kisok ATMs in favor of those at banks for obvious reasons.
Above all else, remember: you will NOT see everything!. You can literally spend years seeing the sights of London alone much less those of the UK, so don't try to take it in all at once by limiting your visits to, say, the British Museum solely to an afternoon. Take your time and enjoy your time away from work, and if you miss something this time you can always catch that particular sight the next time you visit.